Method and apparatus for controlling vibration for hybrid electric vehicle

ABSTRACT

Disclosed are a method of and an apparatus for controlling a vibration of a hybrid electric vehicle. An apparatus for controlling a vibration of a hybrid electric vehicle may include: an engine position detector detecting a position of an engine; an air amount detector detecting an air amount flowing into the engine; an accelerator pedal position detector detecting a position of an accelerator pedal; a vehicle speed detector detecting a speed of the hybrid electric vehicle; and a controller. The controller controls the operation of a motor based on the position of the engine, the air amount, the position of the accelerator pedal, and the speed of the hybrid electric vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2016-0169476 filed in the Korean IntellectualProperty Office on Dec. 13, 2016, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE DISCLOSURE (a) Field of the Disclosure

The present disclosure relates to a method of and an apparatus forcontrolling a vibration of a hybrid electric vehicle.

(b) Description of the Related Art

As is generally known in the art, a hybrid electric vehicle (HEV) usesan internal combustion engine and a battery power source together. Inother words, the hybrid electric vehicle efficiently combines and usespower of the internal combustion engine and power of a driving motor.Since the hybrid electric vehicle uses both mechanical energy of theengine and electrical energy of the battery, uses optimal operationregions of the engine and the driving motor, and recovers energy uponbraking, fuel efficiency may be improved and the energy may beefficiently used.

The hybrid electric vehicle provides driving in an electric vehicle (EV)mode in which only torque of the driving motor is used; a hybridelectric vehicle (HEV) mode in which torque of the engine is used asmain torque and torque of the driving motor is used as auxiliary torque;and a regenerative braking mode in which braking and inertial energy arerecovered through electrical power generation of the driving motorduring braking of the vehicle or during deceleration of the vehicle byinertia to be charged in the battery.

The vibration may be caused in a power system of the hybrid electricvehicle due to several factors, and a vibration component is mostlyextracted using a frequency analysis method. In conventional frequencyanalysis, an analog method using a bandpass filter has been used, and inthis method, a vibration component is extracted based on a magnitude ofeach point in a frequency band. However, a unique vibration component ofan engine and a noise component are not clearly divided, and excessivevibration suppression control may have a negative influence on controlefficiency and energy management. Further, because a reference signal isgenerated only in a specific frequency component and only asynchronization signal synchronized with a vibration signalcorresponding to the specific frequency component is generated based onthe reference signal, active vibration control of other frequencycomponents that may be additionally caused cannot be performed.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the disclosure andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE DISCLOSURE

The present disclosure has been made in an effort to provide a method ofand an apparatus for controlling a vibration of a hybrid electricvehicle having advantages of being capable of efficiently controlling avibration by reducing a calculation load of a controller and byselecting a control target frequency using Walsh-based Discrete FourierTransform (WDFT).

A method of controlling a vibration of a hybrid electric vehicleaccording to an exemplary embodiment of the present disclosure mayinclude: calculating an engine speed based on a position of an engine;setting a reference angle based on the position of the engine; setting awindow for performing Walsh-based Discrete Fourier Transform (WDFT)based on the reference angle; calculating a magnitude spectrum and aphase spectrum by performing the WDFT based on the engine speed, thereference angle, and the window; selecting a control target frequencybased on the magnitude spectrum; compensating a magnitude of the controltarget frequency generating a reference signal based on the magnitudeand a phase of the control target frequency; determining a magnituderatio of the reference signal based on the engine speed and an engineload; calculating a command torque by applying the magnitude ratio andan engine torque to the reference signal; calculating an inverse phasetorque of the command torque; correcting the inverse phase torque basedon the engine load; and controlling operation of a motor to generate thecorrected inverse phase torque.

The correcting of the inverse phase torque may include decreasing theinverse phase torque by applying a predetermined offset to the inversephase torque when the engine load is greater than a predetermined load.

The selecting of the control target frequency may include: setting areference spectrum based on the engine speed and the engine load; andselecting the control target frequency by comparing the referencespectrum and the magnitude spectrum.

The reference spectrum may be a set of reference values at eachfrequency, and a specific frequency may be selected as the controltarget frequency when a magnitude corresponding to the specificfrequency is greater than the reference value corresponding to thespecific frequency.

The magnitude of the control target frequency may be compensated byapplying a scale factor to the control target frequency.

The generating of the reference signal may include performing InverseWalsh-based Discrete Fourier Transform (IWDFT) based on the magnitudeand the phase of the control target frequency.

The method may further include compensating the phase of the controltarget frequency by applying a compensation phase to the phase of thecontrol target frequency.

The window may be determined according to the number of cylinders andthe number of strokes of the engine.

The engine load may be calculated based on an air amount flowing intothe engine.

The engine torque may be calculated based on a position of anaccelerator pedal and a speed of the hybrid electric vehicle.

The engine may be a two-cylinder four-stroke engine.

A method of controlling a vibration of a hybrid electric vehicleaccording to another exemplary embodiment of the present disclosure mayinclude: calculating a motor speed based on a position of a motor;setting a reference angle based on the position of the motor; setting awindow for performing Walsh-based Discrete Fourier Transform (WDFT)based on the reference angle; calculating a magnitude spectrum and aphase spectrum by performing the WDFT based on the motor speed, thereference angle, and the window; selecting a control target frequencybased on the magnitude spectrum; compensating a magnitude of the controltarget frequency by applying a scale factor to the control targetfrequency; generating a reference signal by performing InverseWalsh-based Discrete Fourier Transform (IWDFT) based on the magnitudeand a phase of the control target frequency; determining a magnituderatio of the reference signal based on an engine speed and an engineload; calculating a command torque by applying the magnitude ratio andan engine torque to the reference signal; calculating an inverse phasetorque of the command torque; correcting the inverse phase torque basedon the engine load; and controlling operation of the motor to generatethe corrected inverse phase torque.

The correcting of the inverse phase torque may include decreasing theinverse phase torque by applying a predetermined offset to the inversephase torque when the engine load is greater than a predetermined load.

The selecting of the control target frequency may include: setting areference spectrum based on the engine speed and the engine load; andselecting the control target frequency by comparing the referencespectrum and the magnitude spectrum.

The reference spectrum may be a set of reference values at eachfrequency, and a specific frequency may be selected as the controltarget frequency when a magnitude corresponding to the specificfrequency is greater than the reference value corresponding to thespecific frequency.

The method may further include compensating the phase of the controltarget frequency by applying a compensation phase to the phase of thecontrol target frequency.

The window may be determined according to the number of cylinders andthe number of strokes of the engine.

Thee engine load may be calculated based on an air amount flowing intothe engine.

The engine torque may be calculated based on a position of anaccelerator pedal and a speed of the hybrid electric vehicle.

The engine may be a two-cylinder four-stroke engine.

According to an exemplary embodiment of the present disclosure, acalculation load of a controller may be reduced using Walsh-basedDiscrete Fourier Transform (WDFT). In addition, by selecting a controltarget frequency, efficient vibration control may be performed. Further,an inverse phase torque is decreased by applying a predetermined offsetto the inverse phase torque when an engine is in a high load state,thereby improving energy efficiency of the hybrid electric vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a hybrid electric vehicleaccording to an exemplary embodiment of the present disclosure.

FIG. 2 is a block diagram illustrating an apparatus for controlling avibration of a hybrid electric vehicle according to an exemplaryembodiment of the present disclosure.

FIG. 3 is a flowchart illustrating a method of controlling a vibrationof a hybrid electric vehicle according to an exemplary embodiment of thepresent disclosure.

FIG. 4 is a graph illustrating a method of setting a reference angle anda window according to an exemplary embodiment of the present disclosure.

FIG. 5 is a graph illustrating a Walsh function according to anexemplary embodiment of the present disclosure.

FIG. 6 is a graph illustrating a magnitude spectrum and a phase spectrumwhen a Discrete Fourier Transform is performed.

FIG. 7 is a graph illustrating a magnitude spectrum and a phase spectrumwhen a Walsh-based Discrete Fourier Transform is performed according toan exemplary embodiment of the present disclosure.

FIG. 8 is a graph illustrating comparing results obtained by performinga Walsh-based Discrete Transform and a Discrete Fourier Transformaccording to an exemplary embodiment of the present disclosure.

FIG. 9 is a graph illustrating a reference spectrum according to anexemplary embodiment of the present disclosure.

FIG. 10 is a graph illustrating an inverse phase torque according to anexemplary embodiment of the present disclosure.

FIG. 11 is a graph illustrating a state in which a magnitude of acontrol target frequency is reduced according to an exemplary embodimentof the present disclosure.

FIG. 12 is a flowchart illustrating a method of controlling a vibrationof a hybrid electric vehicle according to another exemplary embodimentof the present disclosure

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present disclosure will be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the disclosure are shown. However, the present disclosure is notlimited to the exemplary embodiments described herein, and may bemodified in various different ways.

The drawings and description are to be regarded as illustrative innature and not restrictive. Like reference numerals designate likeelements throughout the specification.

The configurations illustrated in the drawings are arbitrarily shown forbetter understanding and ease of description, but the present disclosureis not limited thereto.

FIG. 1 is a block diagram illustrating a hybrid electric vehicleaccording to an exemplary embodiment of the present disclosure.

As shown in FIG. 1, a hybrid electric vehicle according to an exemplaryembodiment of the present disclosure includes an engine 10, a motor 20,an engine clutch 30, a transmission 40, a battery 50, a hybrid starter &generator (HSG) 60, a differential gear device 70, a wheel 80, and acontroller 100.

The engine 10 combusts a fuel to generate torque, and various enginessuch as a gasoline engine and a diesel engine may be used as the engine10. The engine 10 may be a two-cylinder four-stroke engine. In atwo-cylinder engine, by reducing a size of the engine 10, fuelconsumption may be enhanced, but because the two-cylinder engine has aproblem in that vibration is excessive, a method of controllingvibration according to an exemplary embodiment of the present disclosureto be described below may be performed.

The motor 20 is disposed between the transmission 40 and the battery 50and generates torque using electricity of the battery 50.

The engine clutch 30 is disposed between the engine 10 and the motor 20and selectively connects the engine 10 to the motor 20.

The hybrid electric vehicle provides driving in an electric vehicle (EV)mode in which only torque of the motor 20 is used, a hybrid electricvehicle (HEV) mode in which torque of the engine 10 is used as maintorque and torque of the motor 20 is used as auxiliary torque, and aregenerative braking mode in which braking and inertial energy arerecovered through electrical power generation of the motor 20 duringbraking of the vehicle or during deceleration of the vehicle by inertiato be charged in the battery 50.

For torque transmission of the hybrid electric vehicle, torque generatedby the engine 10 and/or the motor 20 is transmitted to an input shaft ofthe transmission 40, and torque output from an output shaft of thetransmission 40 is transmitted to an axle via the differential geardevice 70. The axle rotates the wheel 80 such that the hybrid electricvehicle runs by the torque generated by the engine 10 and/or the motor20.

The battery 50 may supply electricity to the motor 20 in the EV mode andthe HEV mode, and may be charged with electricity recovered through themotor 20 in the regenerative braking mode.

The HSG 60 may start the engine 10 or generate electricity according toan output of the engine 10.

The controller 100 controls operations of the engine 10, the motor 20,the engine clutch 30, the transmission 40, the battery 50, and the HSG60. The controller 100 may be implemented with at least one processorexecuted by a predetermined program. The predetermined program mayinclude a series of commands for performing each step included in amethod of controlling a vibration of a hybrid electric vehicle accordingto an exemplary embodiment of the present disclosure to be describedbelow.

The above-described hybrid electric vehicle is one example to which thespirit of the present disclosure may be applied, and the spirit of thepresent disclosure may be applied to various hybrid electric vehicles aswell as the hybrid electric vehicle shown in FIG. 1.

FIG. 2 is a block diagram illustrating an apparatus for controlling avibration of a hybrid electric vehicle according to an exemplaryembodiment of the present disclosure.

As shown in FIG. 2, an apparatus for controlling a vibration of a hybridelectric vehicle according to an exemplary embodiment of the presentdisclosure may include a data detector 90, the controller 100, and themotor 20.

The data detector 90 may include an engine position detector 91, a motorposition detector 92, an air amount detector 93, an accelerator pedalposition detector 94, and a vehicle speed detector 95. The data detector90 may further include other detectors (e.g., a brake pedal positiondetector and the like) for controlling the hybrid electric vehicle.

The engine position detector 91 detects a position of the engine 10 andtransmits a signal corresponding thereto to the controller 100. Theengine position detector 91 may be a crankshaft position sensor thatdetects a rotational angle of a crankshaft of the engine 10. Thecontroller 100 may calculate an engine speed based on the position ofthe engine 10.

The motor position detector 92 detects a position of the motor 20 andtransmits a signal corresponding thereto to the controller 100. Themotor position detector 92 may be a resolver that detects a rotationalangle of a rotor of the motor 20. The controller 100 may calculate amotor speed based on the position of the motor 20.

The air amount detector 93 detects an air amount flowing into the engine10 and transmits a signal corresponding thereto to the controller 100.The controller 100 may calculate an engine load based on the air amount.

The accelerator pedal position detector 94 detects a position of anaccelerator pedal (i.e., a pushed degree of the accelerator pedal) andtransmits a signal corresponding thereto to the controller 100. When theaccelerator pedal is pushed completely, the position of the acceleratorpedal is 100%, and when the accelerator pedal is not pushed, theposition of the accelerator pedal is 0%.

The vehicle speed detector 95 detects a speed of the hybrid electricvehicle and transmits a signal corresponding thereto to the controller100. The controller 100 may calculate an engine torque based on theposition of the accelerator pedal and the speed of the hybrid electricvehicle.

By controlling operation of the motor 20 based on the data detected bythe data detector 90, the controller 100 may control a vibration of theengine 10.

Hereinafter, a method of controlling a vibration of a hybrid electricvehicle according to an exemplary embodiment of the present disclosurewill be described in detail with reference to FIGS. 3 to 11.

FIG. 3 is a flowchart illustrating a method of controlling a vibrationof a hybrid electric vehicle according to an exemplary embodiment of thepresent disclosure. FIG. 4 is a graph illustrating a method of setting areference angle and a window according to an exemplary embodiment of thepresent disclosure. FIG. 5 is a graph illustrating a Walsh functionaccording to an exemplary embodiment of the present disclosure. FIG. 6is a graph illustrating a magnitude spectrum and a phase spectrum whenDiscrete Fourier Transform is performed. FIG. 7 is a graph illustratinga magnitude spectrum and a phase spectrum when a Walsh-based DiscreteFourier Transform is performed according to an exemplary embodiment ofthe present disclosure. FIG. 8 is a graph illustrating comparing resultsobtained by performing Walsh-based Discrete Transform and DiscreteFourier Transform according to an exemplary embodiment of the presentdisclosure. FIG. 9 is a graph illustrating a reference spectrumaccording to an exemplary embodiment of the present disclosure. FIG. 10is a graph illustrating an inverse phase torque according to anexemplary embodiment of the present disclosure. FIG. 11 is a graphillustrating a state in which a magnitude of a control target frequencyis reduced according to an exemplary embodiment of the presentdisclosure.

As shown in FIG. 3, the controller 100 calculates an engine speed basedon a position of the engine 10 at step S101. The controller 100 mayreceive the position of the engine 10 detected by the engine positiondetector 91 and calculate the engine speed by differentiating theposition of the engine 10. As shown in FIG. 4, when the engine 10 is atwo-cylinder four-stroke engine, while the engine 10 rotates twice, anexplosion occurs once in each cylinder.

The controller 100 sets a reference angle based on the position of theengine 10 at step S102. The reference angle means a start time point forperforming Walsh-based Discrete Fourier Transform (WDFT) to be describedbelow. For example, as shown in FIG. 4, the controller 100 may set anangle between top dead center (TDC) and bottom dead center (BDC) of afirst cylinder 10 a to the reference angle. Alternatively, an anglebetween top dead center (TDC) and bottom dead center (BDC) of a secondcylinder 10 b may be set to the reference angle.

The controller 100 sets a window for performing the WDFT based on thereference angle at step S103. The window may be determined according tospecifications (e.g., the number of cylinders and the number of strokes)of the engine 10. Since explosion occurs once in each cylinder while theengine 10 rotates twice, the window may be set to 720°. In terms of afrequency, because two peaks exist within the window, two explosionswhile the engine 10 rotates twice may be expressed by 2 Hz. In otherwords, a primary vibration component (referred to as “C1” in the art)corresponding to the frequency of 2 Hz may be major component of avibration occurring by explosion of the engine 10. Harmonic componentsC0.5, C1.5, C2, C2.5, C3, and C3.5 of the primary vibration componentmay be a cause of the vibration. In this specification, the harmoniccomponents C0.5, C1.5, C2, C2.5, C3, and C3.5 are considered to reducethe vibration, but the present disclosure is not limited thereto. Inother words, in order to control the vibration of the engine 10, otherharmonic components (e.g., C4, C4.5, C5, and the like) may be furtherconsidered.

By performing the WDFT based on the engine speed, the reference angle,and the window, the controller 100 calculates a magnitude spectrum ofMC0.5 to MC3.5 and a phase spectrum of θC0.5 to θC3.5 at step S104.

Hereinafter, the WDFT will be described by comparing it with a DiscreteFourier Transform (DFT).

The DFT may be used when calculating a frequency spectrum.

When the N number of discrete signals x[n] (n=1, 2, . . . , and N) aregiven, DFT of x[n] is defined as in Equation 1.

$\begin{matrix}{{X\lbrack k\rbrack}\; = \; {\sum\limits_{n\; = \; 1}^{N}\; {{X\lbrack n\rbrack}\; W_{N}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Herein, W_(N)=e^(−j2πkn/N), and k is a frequency (k=1, 2, . . . and N).

In addition, Equation 1 may be expressed by Equation 2.

$\begin{matrix}{{X\lbrack k\rbrack} = {{\sum\limits_{n = 1}^{N}{{X\lbrack n\rbrack}e^{{- j}\; 2\pi \; {{kn}/N}}}} = {\sum\limits_{n = 1}^{N}{{X\lbrack n\rbrack}\left( {{\cos \frac{2\pi \; {kn}}{N}} - {j\; \sin \frac{2\pi \; {kn}}{N}}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Herein,

$a = {{\sum\limits_{n\; = \; 1}^{N}{{X\lbrack n\rbrack}\mspace{11mu} \cos \; \frac{2\; \pi \; {kn}}{N}\mspace{14mu} {and}\mspace{14mu} b}} = {\sum\limits_{n\; = \; 1}^{N}\; {{X\lbrack n\rbrack}\mspace{11mu} \sin \; {\frac{2\; \pi \; {kn}}{N}.}}}}$

When analyzing a frequency spectrum of a specific frequency k of ananalysis target signal x[n] using the DFT, a magnitude of the specificfrequency k is calculated as in Equation 3.

Magnitude=√{square root over (a ² +b ²)}  [Equation 3]

In addition, a phase of the specific frequency k is calculated as inEquation 4.

$\begin{matrix}{{Phase} = {\tan^{- 1}\; \frac{b}{a}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Upon frequency analyzing a frequency spectrum, when the DFT is used, acalculation load of the controller 100 increases in order to process atriangle function, and a lot of resources of the controller 100 areconsumed in order to process continuous signals at a high speed in realtime.

Therefore, in order to reduce a calculation load of the controller 100,an apparatus for controlling a vibration of a hybrid electric vehicleaccording to an exemplary embodiment of the present disclosure mayanalyze a frequency spectrum using the WDFT.

As shown in FIG. 5, a Walsh function is arranged in an increase order ofthe zero crossing number per unit time. The Walsh function forms a setwith a function of m=2^(n) (n=1, 2, 3, . . . ). FIG. 5 represent a Walshfunction when m=8. The Walsh function is configured with two functionshaving characteristics of sine wave symmetry and cosine wave symmetrylike a Fourier function, and a set of a Walsh function of sine wavesymmetry is referred to as a SAL function and a set of a Walsh functionof cosine wave symmetry is referred to as a CAL function. In otherwords, a sine wave component of Equation 2 may be replaced by the SALfunction, and a cosine wave component of Equation 2 may be replaced bythe CAL function. The WDFT of an analysis target signal x[n] is definedas in Equation 5.

$\begin{matrix}{{X\lbrack k\rbrack} = {\sum\limits_{n\; = \; 1}^{N}{{X\lbrack n\rbrack}\left( {{{CAL}\; \frac{2\; \pi \; {kn}}{N}}\; - \; {j\mspace{11mu} {SAL}\; \frac{2\; \pi \; {kn}}{N}}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Because the Walsh function has only a value of 1 or −1, frequencyspectrum analysis may be performed with simple addition and subtraction.

For example, the WDFT of a frequency of 1 Hz component may be expressedby Equation 6.

$\begin{matrix}{{X\lbrack 1\rbrack} = {\sum\limits_{n\; = \; 1}^{N}{{X\lbrack n\rbrack}\left( {{{CAL}\; \frac{2\; \pi \; n}{N}}\; - \; {j\mspace{11mu} {SAL}\; \frac{2\; \pi \; n}{N}}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Herein,

${a = {{\sum\limits_{n = 1}^{N/4}{X\lbrack n\rbrack}} - {\sum\limits_{{({N/4})} + 1}^{N/2}{X\lbrack n\rbrack}} - {\sum\limits_{{({N/2})} + 1}^{3{N/4}}{X\lbrack n\rbrack}} + {\sum\limits_{{({3{N/4}})} + 1}^{N}{X\lbrack n\rbrack}}}},{and}$$b = {{\sum\limits_{n = 1}^{N/4}{X\lbrack n\rbrack}} + {\sum\limits_{{({N/4})} + 1}^{N/2}{X\lbrack n\rbrack}} - {\sum\limits_{{({N/2})} + 1}^{3{N/4}}{X\lbrack n\rbrack}} - {\sum\limits_{{({3{N/4}})} + 1}^{N}{{X\lbrack n\rbrack}.}}}$

In other words, when analyzing a frequency spectrum of a specificfrequency k of an analysis target signal x[n] using WDFT, a magnitude ofthe specific frequency k is calculated as in Equation 7.

Magnitude=|a|+|b|  [Equation 7]

In addition, a phase of the specific frequency k is calculated as inEquation 8.

$\begin{matrix}{{Phase} = {\tan^{- 1}\; \frac{b}{a}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

As shown in FIGS. 6 to 8, it may be verified that a magnitude spectrumand a phase spectrum calculated by performing the DFT and a magnitudespectrum and a phase spectrum calculated by performing the WDFT aresubstantially similar.

Therefore, in a method of controlling a vibration according to anexemplary embodiment of the present disclosure, a magnitude spectrum anda phase spectrum are calculated by performing the WDFT instead of theDFT. A calculation load of the controller 100 increases in order tocalculate a magnitude spectrum and a phase spectrum by performing theDFT, but when performing the WDFT, the controller 100 may quicklycalculate the magnitude spectrum and the phase spectrum.

The controller 100 sets a reference spectrum Ref_(C0.05) to Ref_(C3.5)based on the engine speed and the engine load at step S105. Thecontroller 100 may calculate the engine speed based on a signal of theengine position detector 91 and calculate the engine load based on asignal of the air amount detector 93. The reference spectrum is a set ofreference values Ref_(C0.5) to Ref_(C3.5) at each frequency fordetermining whether to select a specific frequency as a control targetfrequency. For example, the controller 100 may set the referencespectrum using a map table in which a reference spectrum according tothe engine speed and the engine load is set. As shown in FIG. 9, areference value Ref_(C1) corresponding to the primary vibrationcomponent and a reference value Ref_(C2) corresponding to the secondaryvibration component may be differently set.

The controller 100 compares the reference spectrum and the magnitudespectrum to select a control target frequency at step S106. When amagnitude M corresponding to a specific frequency is greater than areference value Ref corresponding to the specific frequency, thespecific frequency is selected as the control target frequency. As shownin FIG. 9, when a magnitude M_(C1) corresponding to C1 is greater than areference value Ref_(C1) corresponding to the C1, the C1 is selected asthe control target frequency. When a magnitude M_(C1) corresponding toC2 is equal to or less than a reference value Ref_(C2) corresponding tothe C2, the C2 is not selected as the control target frequency. When amagnitude M_(C3) corresponding to C3 is greater than a reference valueRef_(C3) corresponding to the C3, the C3 is selected as the controltarget frequency.

The controller 100 may compensate a magnitude and a phase of the controltarget frequency at step S107. As described above, because resultsobtained by performing the WDFT and the DFT are similar but are not thesame, the controller 100 may compensate the magnitude of the controltarget frequency by applying a scale factor F_(C0.5) to F_(C3.5) to themagnitude of the control target frequency. In addition, the controller100 may compensate the phase of the control target frequency by applyinga compensation phase P_(C0.5) to P_(C3.5) to the phase of the controltarget frequency. The scale factor F_(C0.5) to F_(C3.5) and thecompensation phase P_(C0.5) to P_(C3.5) may be previously set by aperson of ordinary skill in the art in consideration of the resultsobtained by performing the WDFT and the DFT. Since the C1 and the C3 areselected as the control target frequency at step S106, a compensatedmagnitude of C1 becomes F_(C1)×M_(C1), and a compensated phase thereofbecomes θ_(C1)+P_(C1). In addition, a compensated magnitude of the C3becomes F_(C3)×M_(C3), and a compensated phase thereof becomesθ_(C3)+P_(C3).

The controller 100 performs an Inverse Walsh-based Discrete FourierTransform (IWDFT) based on a magnitude and a phase of the control targetfrequency to generate a reference signal S_(y) at step S108. The IWDFTis known, and thus a detailed description thereof will be omitted.

The controller 100 determines a magnitude ratio A_(y) of the referencesignal based on the engine speed and the engine load at step S109. Forexample, the controller 100 may determine the magnitude ratio using amap table in which a magnitude ratio according to the engine speed andthe engine load is set. A magnitude ratio for reducing a vibration ofthe engine 10 is previously set in the map table.

By applying the magnitude ratio A_(y) and the engine torque T_(Eng) tothe reference signal S_(y), the controller 100 calculates a commandtorque T_(Mot)=A_(y)×S_(y)×T_(Eng) at step S110.

The controller 100 calculates an inverse phase torque −T_(Mot) of thecommand torque at step S111. The controller 100 may control operation ofthe motor 20 to generate the inverse phase torque −T_(Mot) such that thevibration of the engine 10 is controlled.

Meanwhile, the controller 100 may correct the inverse phase torque−T_(Mot) based on the engine load at step S112. In detail, as shown inFIG. 10, when the engine load is greater than a predetermined load, thecontroller 100 may decrease the inverse phase torque by applying apredetermined offset to the inverse phase torque. In other words,compared to a low load state, the hybrid electric vehicle is notsignificantly affected by the vibration of the engine 10 when the engine10 is in a high load state. Therefore, the inverse phase torque isdecreased and residual energy due to a decrease of the torque is used tocharge the battery 50 to improve energy efficiency of the hybridelectric vehicle. The predetermined offset may be set to a value whichis determined by a person of ordinary skill in the art based on theengine load. Accordingly, the controller 100 controls operation of themotor 20 to generate the corrected inverse phase torque such that thevibration of the engine 10 is controlled and the energy efficiency ofthe hybrid electric vehicle is improved.

According to an exemplary embodiment of the present disclosure, as shownin FIG. 11, it may be verified that a magnitude of a control targetfrequency (e.g., C1 and C3) is reduced.

Hereinafter, a method of controlling a vibration of a hybrid electricvehicle according to another exemplary embodiment of the presentdisclosure will be described with reference to FIG. 12.

FIG. 12 is a flowchart illustrating a method of controlling a vibrationof a hybrid electric vehicle according to another exemplary embodimentof the present disclosure.

Referring to FIG. 12, a method of controlling a vibration of a hybridelectric vehicle according to another exemplary embodiment of thepresent disclosure is similar to a method of controlling a vibration ofa hybrid electric vehicle according to an exemplary embodiment of thepresent disclosure, except for use of a position of the motor 10 insteadof a position of the engine 10.

As shown in FIG. 12, the controller 100 calculates a motor speed basedon a position of the motor 20 at step S201. The controller 100 mayreceive a position of the motor 20 detected by the motor positiondetector 92 and calculate a motor speed by differentiating the positionof the motor 20.

The controller 100 sets a reference signal based on the position of themotor 20 at step S202. The controller 100 may divide a signal of themotor position detector 92 according to the number of poles of the motor20. For example, when the motor 20 is a 16-pole motor, by dividing asignal of the motor position detector 92 into eight, the controller 100may set a specific time point to the reference angle.

In a state in which the engine 10 is connected to the motor 20 by theengine clutch 30, because the motor 20 rotates according to a rotationof the engine 10, steps S203 to S212 are the same as steps S103 to S112and therefore a detailed description thereof will be omitted.

As described above, according to an exemplary embodiment of the presentdisclosure, the calculation load of the controller 100 may be reducedusing the WDFT. In addition, by selecting a control target frequency,efficient vibration control may be performed. Further, the inverse phasetorque is decreased by applying the predetermined offset to the inversephase torque when the engine 10 is in the high load state, therebyimproving energy efficiency of the hybrid electric vehicle.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the disclosure is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of controlling a vibration of a hybridelectric vehicle, the method comprising calculating an engine speedbased on a position of an engine; setting a reference angle based on theposition of the engine; setting a window for performing Walsh-basedDiscrete Fourier Transform (WDFT) based on the reference angle;calculating a magnitude spectrum and a phase spectrum by performing theWDFT based on the engine speed, the reference angle, and the window;selecting a control target frequency based on the magnitude spectrum;compensating a magnitude of the control target frequency; generating areference signal based on the magnitude and a phase of the controltarget frequency; determining a magnitude ratio of the reference signalbased on the engine speed and an engine load; calculating a commandtorque by applying the magnitude ratio and an engine torque to thereference signal; calculating an inverse phase torque of the commandtorque; correcting the inverse phase torque based on the engine load;and controlling operation of a motor to generate the corrected inversephase torque.
 2. The method of claim 1, wherein the correcting of theinverse phase torque comprises: decreasing the inverse phase torque byapplying a predetermined offset to the inverse phase torque when theengine load is greater than a predetermined load.
 3. The method of claim1, wherein the selecting of the control target frequency comprises:setting a reference spectrum based on the engine speed and the engineload; and selecting the control target frequency by comparing thereference spectrum and the magnitude spectrum.
 4. The method of claim 3,wherein the reference spectrum is a set of reference values at eachfrequency, and a specific frequency is selected as the control targetfrequency when a magnitude corresponding to the specific frequency isgreater than the reference value corresponding to the specificfrequency.
 5. The method of claim 1, wherein the magnitude of thecontrol target frequency is compensated by applying a scale factor tothe control target frequency.
 6. The method of claim 1, wherein thegenerating of the reference signal comprises performing InverseWalsh-based Discrete Fourier Transform (IWDFT) based on the magnitudeand the phase of the control target frequency.
 7. The method of claim 1,further comprising compensating the phase of the control targetfrequency by applying a compensation phase to the phase of the controltarget frequency.
 8. The method of claim 1, wherein the window isdetermined according to the number of cylinders and the number ofstrokes of the engine.
 9. The method of claim 1, wherein the engine loadis calculated based on an air amount flowing into the engine.
 10. Themethod of claim 1, wherein the engine torque is calculated based on aposition of an accelerator pedal and a speed of the hybrid electricvehicle.
 11. The method of claim 1, wherein the engine is a two-cylinderfour-stroke engine.
 12. A method of controlling a vibration of a hybridelectric vehicle, the method comprising: calculating a motor speed basedon a position of a motor; setting a reference angle based on theposition of the motor; setting a window for performing Walsh-basedDiscrete Fourier Transform (WDFT) based on the reference angle;calculating a magnitude spectrum and a phase spectrum by performing theWDFT based on the motor speed, the reference angle, and the window;selecting a control target frequency based on the magnitude spectrum;compensating a magnitude of the control target frequency by applying ascale factor to the control target frequency; generating a referencesignal by performing Inverse Walsh-based Discrete Fourier Transform(IWDFT) based on the magnitude and a phase of the control targetfrequency; determining a magnitude ratio of the reference signal basedon an engine speed and an engine load; calculating a command torque byapplying the magnitude ratio and an engine torque to the referencesignal; calculating an inverse phase torque of the command torque;correcting the inverse phase torque based on the engine load; andcontrolling operation of the motor to generate the corrected inversephase torque.
 13. The method of claim 12, wherein the correcting of theinverse phase torque comprises: decreasing the inverse phase torque byapplying a predetermined offset to the inverse phase torque when theengine load is greater than a predetermined load.
 14. The method ofclaim 12, wherein the selecting of the control target frequencycomprises: setting a reference spectrum based on the engine speed andthe engine load; and selecting the control target frequency by comparingthe reference spectrum and the magnitude spectrum.
 15. The method ofclaim 14, wherein the reference spectrum is a set of reference values ateach frequency, and a specific frequency is selected as the controltarget frequency when a magnitude corresponding to the specificfrequency is greater than the reference value corresponding to thespecific frequency.
 16. The method of claim 12, further comprisingcompensating the phase of the control target frequency by applying acompensation phase to the phase of the control target frequency.
 17. Themethod of claim 12, wherein the window is determined according to thenumber of cylinders and the number of strokes of the engine.
 18. Themethod of claim 12, wherein the engine load is calculated based on anair amount flowing into the engine.
 19. The method of claim 12, whereinthe engine torque is calculated based on a position of an acceleratorpedal and a speed of the hybrid electric vehicle.
 20. The method ofclaim 12, wherein the engine is a two-cylinder four-stroke engine.